Build your vocab!! Yes, it may not be as important in the new version, but it will still be crucial for a good CR score. Just look at the ACT-- many questions & answers include “SAT-style vocab” so you won’t know what to pick if you don’t know the words! Start lighter-- choose vocab books with easier words to get a good base, and then work upwards. Don’t bother learning words like antediluvian for now.
Why not practice math now? On the current SAT you need to be almost flawless for a 700+ score-- so work on your accuracy. Take timed tests where you worry just as much on accuracy of the easy questions as knowing the stuff in the harder questions.
For the writing, learn your grammar. I suggest Erica Meltzer’s “Ultimate guide” which offers SAT specific advice, but, really, it will still relevant in a year’s time and also for life!
Finally-- as others have been saying-- make the time to read. By reading at least 150 pages per week, you are bound to not only become a better reader and test taker, but also have more to say and comment on in your essays.